Theoretical Modelling of Components of a Solar Thermal Power Plant for Performance Enhancement

Mahmood, Hassan (2020) Theoretical Modelling of Components of a Solar Thermal Power Plant for Performance Enhancement. Doctoral thesis, Northumbria University.

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Abstract

Solar power is a renewable energy source and can meet the growing world demand for electricity. The thermal energy produces by solar is an attractive solution to handle the environmental issues caused by fossil fuels. This research focuses on the theoretical modelling of components of solar thermal power plants for performance enhancement. It involves the modelling of the solar collector and organic Rankine power cycle. The overall solar thermal power plant comprises such components as a collector, evaporator, turbine, condenser, pump, heat exchanger, and thermal storage system. The present research studies the Linear Fresnel Reflector's performance in providing the heat input to the Organic Rankine Cycle and investigate the annual energy production of the power plant, located at the testing site in Almatret, Catalonia, Spain. The work includes step-by-step modification of the actual system design with a performance analysis of the non-concentrating and concentrating power plant systems.

The mathematical model of the ORC was developed based on the thermodynamic equations with simulations performed using MATLAB/Thermolib software. The ORC system performance was investigated for different working fluids at their critical operating conditions. The considered working fluids include the HCFC-245fa, HCFC-134a, Propane, butane, ethanol, and methanol. The ORC model was upgraded by taking into account the heat exchanger to recover the system waste heat, and results were compared to that from a simple ORC model. The recovery of the heat in the cycle increases the thermal efficiency of the ORC, but its benefits depend on the critical parameters of the working fluid. The effect is considerable for R134a and negligible for Ethanol. The Solar Organic Rankine Cycle (SORC) mathematical model was developed, and simulation designed on the MATLAB/Thermolib software. The evacuated tube collector designed for the Almatret latitude position and supplied the power input to the Rankine system. The model based on the water heat transfer fluid of the solar field, and it is transferring the heat to HCFC-134fa, the working fluid of the Rankine cycle via a heat exchanger without a tracking and thermal storage system. The thermal performance of the model investigated base on the day scan results. The solar organic Rankine cycle has an area 600 m2 to generate peak thermal power 71 kW, and the mechanical output power of the Rankine cycle is 4.274 kW using 30 bar evaporation pressure and 10 bar condensation pressure. The Generic Algorithm code developed on MATLAB and connected with the Thermolib model to operate the SORC system with optimum variables and thermal efficiency increases from 10.58 % to 11.87 % using the peak value solar irradiance. Fresnel solar reflector model simulated by using the light tools simulation software and have a one-axis tracking system. The actual weather data was imported to the simulation software to investigate the system performance using the day scan results. The theoretical model derived to determine the system thermal energy and conduction, convection, and radiation heat transfer of the receiver tube. The thermal losses of the model investigated and derived solar angles of the specific day. The tracking system based on the incidence angle modifier model (IAM) and calculated the system optical efficiency corresponds to the IAM in terms of the longitudinal and transverse components of the incidence of rays. The analysis performed from ambient conditions to determine the peak value by using the Therminol-62 working fluid. The LFR field produces 106.425 kW thermal energy during peak hour using a high value of IAM, and the reflector area is 214.38 m2. The thermal losses during the peak time of day at 1:00 PM is 7.872 kW.

The system advisor simulation software used to validate the solar power linear Fresnel system. The complete model simulated with the thermal storage system. The actual weather data and Therminol-62 heat transfer fluid and NOVECTM649 working fluid import to the simulation model. The simulation model based on the exact power plant is located in the Almatret location and investigated the model thermal performance. The results show that the LFR field with a tracking system and Therminol-62 working fluid increases the system thermal performance. The Therminol-62 have high-temperature ranges at low operating pressure as compare to the steam working fluid. The ORC has a higher value of thermal efficiency NOVECTM649 than HCFC-134a and produces 7.2 kW output power of the ORC plant during the peak hour of solar irradiance with specific operating conditions. The two-tank thermal storage system extends the Plant four hours of operation and produces the highest power output of 2160 kWh in July.

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